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Oil is one of the world's main sources of energy, but because it is unevenly distributed it must be transported by ship across oceans and by pipelines across land. This results in accidents when transferring oil to vessels, when transporting oil, and when pipelines break, as well as when drilling for oil. While massive and catastrophic oil spills receive most of the attention, smaller and chronic oil spills and seeps occur regularly. These spills contaminate coasts and estuaries, and they can cause human health problems.

Oil is a mixture of hydrocarbon compounds, which are the decayed remains of marine animals and plants that lived in shallow inland seas, died, and drifted to the bottom. For the past 600 million years, under intense pressure and temperatures, these remains changed into the complicated hydrocarbons called petroleum. Crude oil is a mixture of gas, naphtha, kerosene, light gas, and residuals, which have different health effects.

Overall production of petroleum products rose from about 500 million tons in 1950 to over 2,500 million tons by the mid-1990s, resulting in massive transport and associated oil spills. By far the greatest oil reserves are in the Middle East, and major transportation routes emanate from there. The number of oil spills, both major and minor, has been increasing with the increasing rate of oil transport and the aging of oil tankers, as well as an increase in the size of oil tankers. Oil accounts for over half the tonnage of all sea cargo.

Since the 1960s there have been about twenty oil spills of more than 20 million gallons. Major oil spills have occurred off the coast of Mexico, the Middle East, off South Africa, in the North Pacific, and in Alaska, as well as in the pipeline in Usink, Russia. The largest oil spill to date resulted from the Gulf War in 1991, when over 240 million gallons of oil poured into the Persian Gulf, most of it deliberately. The next largest oil spill, from the Ixtox-1 well off Mexico, involved a blowout of 140 million gallons.

The largest spills do not necessarily receive the most media coverage, either because of their location, the lack of human health or ecological effects, the lack of documentation of these effects, or a lack of media interest. For example the 1980 Nowruz field spill in Arabia (80 million gallons) and the 1992 Fergana Valley spill in Uzbekistan (80 million gallons) barely received any attention. In contrast, two smaller spills received enormous media attention: the oil tanker Amoco Cadiz released 68.7 million gallons off the coast of France in 1978, and the tanker Exxon Valdez spilled 11 million gallons into Prince William Sound in Alaska in 1989.

Short-term public health impacts from oil spills include accidents suffered by those on damaged tankers or those involved in the cleanup, and illnesses caused by toxic fumes or by eating contaminated fish or shellfish. However, there are other less obvious public health impacts, including losses and disruptions of commercial and recreational fisheries, seaweed harvesting, boating, and a variety of other uses of affected water. There are also emotional, aesthetic, and economic losses, such as when Native Americans and others are denied subsistence or recreational uses. In both the case of the Exxon Valdez and the Amoco Cadiz there were permanent changes to the social and cultural communities residing in the region, which had permanent public health consequences, including chronic psychological stress.

JOANNA BURGER

(SEE ALSO: Ambient Water Quality; Ocean Dumping; Pollution)